To me the line is and has been a work in progress since OTA's a work in progress. In no way does that show trouble for either of these guys...If Corbett doesn't get the center spot I look at it like he has had some experience there and he goes back to his guard spot. Evans IMO has no worries either.
IMO you also have to take into consideration we have a new O-Line coach who this early is still feeling his way around and the players as well with him. I think trouble is not the proper term with these players....they are not going to be cut ...to me trouble means out the door.